This invention relates to meat curing processes and to pickling solutions useful therefor.
In the curing of meats it is conventional to employ pickling solutions (brines) based on alkali metal chloride and nitrite ion. The nitrite protects against toxic organisms such as Clostridium botulinum, prevents off-flavor and spoilage by inhibiting oxidation of unsaturated fats, and produces nitric oxide which reacts with substances in the meat to form a pleasing red or bright pink "cured meat" color. It is known that nitrite which does not react in the foregoing manner can be acidified to form nitrous acid, which acid then reacts with secondary amine groups of amino acids or amines in the meat to form carcinogenic nitrosoamines. Similarly, the nitrates optionally present in meat curing compositions can be slowly reduced to nitrites by bacteria in the meat. Any residual nitrite from this source also can form nitrosoamines. Nitrosoamine formation from residual nitrite is accelerated by the high temperatures encountered in the frying of bacon. For this reason, bacon requires more attention than other meat products to reduction of residual nitrite, i.e., nitrite remaining in a cured meat product because of failure to react with the meat during the curing process.
Residual nitrite can be eliminated by the addition to pickling solutions of reducing agents, such as sodium erythorbate. These agents accelerate the curing by reducing nitrite to nitric oxide which either reacts with myoglobin of the meat to form red pigment or leaves the pickle or the meat as a gas. Large proportions of reducing agent, however, can cause too great a loss of nitrite, resulting in lack of protection against toxic organisms, poor meat color and spoilage. Accordingly, the preferred method of eliminating or reducing residual nitrite is to lower the pH of the cured meat product by buffering the pickling solution at a pH of 6.0 or less, using a suitable buffering agent such as an inorganic phosphate. The lower pH favors the formation of products which do not promote nitrosoamine formation. The pH, however, cannot be lowered less than 5.5 because, by so doing, too much of the nitrite is decomposed and is lost from the solution as a gas or other decomposition product. The pickling solution is then considered unstable and cannot be used effectively. Lowered nitrite content also reduces protection against C. botulinum and other toxic microorganisms. Experience has shown that the most desirable pickle solution pH for eliminating or minimizing residual nitrite in cured meat products is in the range of 5.5 to 6.0, more preferably 5.65 to 5.9.
The patent literature describes a variety of approaches for the curing of meat products involving the use of pickling solutions containing inorganic phosphates. U.S. Pat. No. 2,823,132 to Sair discloses a pickling solution containing an ascorbate and sodium hexametaphosphate and having a pH of 4.8; this solution is said to be unsuitable due to a lack of storage stability. U.S. Pat. No. 3,104,978 to Elder discloses the use of hydrated crystalline and glassy phosphates in meat curing compositions wherein the phosphate has a Na.sub.2 O/P.sub.2 O.sub.5 ratio of between about 1.8/1 and 1.95/1. U.S. Pat. No. 3,741,777 to Wrobel et al teaches meat curing pickles containing a polyphosphate having a Na.sub.2 O/P.sub.2 O.sub.5 ratio of about 0.9/1 to 2.0/1, such as sodium hexametaphosphate (SHMP) or a combination of SHMP and sodium tripolyphosphate (STPP). U.S. Pat. No. 3,780,192 to Danner et al teaches the use, generally, of food phosphates in meat curing processes. U.S. Pat. No. 3,782,975 to Zyss teaches the use of potassium phosphates for meat curing. U.S. Pat. No. 3,595,679 to Schoch et al is similar to Wrobel et al in the teaching of meat curing pickles containing an edible polyphosphate such as SHMP alone or admixed with STPP. U.S. Pat. No. 4,315,015 to Theiler reviews the problem of residual nitrite and relationship to pickle solution pH. STPP is disclosed as a suitable buffering agent to stabilize the nitrite in the curing solution. U.S. Pat. No. 3,966,974 to Bharucka et al advocates the use of organic nitrites to avoid nitrosoamine formation in meat curing processes. U.S. Pat. No. 3,401,046 to Mahon uses a hydratable phosphate such as STPP, fully hydrated by a sodium nitrite solution, in a meat curing composition, wherein the Na.sub.20 /P.sub.2 O.sub.5 ratio of the phosphate is about 1.67/1 to about 3/1. In addition, a commercial product comprising a 95/5% by weight blend of SHMP and sodium bicarbonate, presumably the subject of U.S. Pat. No. 4,543,260, has been promoted for its ability to reduce nitrite in bacon by producing a more acidic condition than is achieved by conventional alkaline phosphates.
The most successful curing pickles represented by the foregoing patents and commercial practice are those employing mixtures of two or more phosphates or a mixture of a glassy phosphate and an alkaline material such as sodium bicarbonate. Such mixtures, however, require careful attention to the mixing process to avoid errors in mixing proportions, to avoid segregation or caking of components during mixing or storage, and to minimize decomposition of one or more of the materials. Furthermore, the mixing is an additional step which adds to the complexity and cost of the total meat curing process.